Does this Taylor Made Systems link show the required part?
When I replaced the screw cover on my 2000 380DA because the length of the existing part shrunk, exposing the ends, I cut the ends at an angle, matching the angle within the cavity, so I could maximize the length of the new part, using the full available length within the screw cover cavity.
http://www.taylormarine.com/hardware/parts/screwCover/index.html